It is known to construct from precast concrete blocks or crib units, various types of wall structures for a wide range of purposes. Thus, walls may be erected which serve as space barriers, sound barriers, retaining walls, sea walls, dams, flood control walls, bridge abutments and the like. In certain applications low or inconsequential wall loadings are encountered, as for example, a simple sound barrier structure. In other structures of this type, e.g., a sea wall backed by a substantial landside fill, severe loadings are expected and may be made even more pronounced by the presence of a vehicular roadway or railroad right of way constructed on the fill side adjacent the sea wall. In the last-mentioned example of wall structure, wave action exerts heavy loading on one side of the wall, whereas, very significant earth pressures act on the other side of the wall. Types of crib units or blocks as are known for use in such structures are not entirely satisfactory for such service, principally because they do not possess sufficient ruggedness or strength to resist the various force components applied thereto in service. Thus individual or even plural ones of the crib blocks can fail under loading as where a facing panel at one side of the wall and forming one element of the crib unit shears or fractures from the cross member connecting it with another panel at the other side of the wall. The Huntoon U.S. Pat. No. 1,909,539 discloses a type of crib block which would not be satisfactory for use in the heavy loadings situation discussed above. Such block includes a front stretcher piece and rear stretcher member joined by a cross-member or header. The stretcher members are each relatively thin and the rear stretcher is considerably shorter than the front. Further, the header is relatively narrow and meets in juncture with the stretchers in somewhat sharp juncture so that the cantilevering effect of horizontal transverse force components acting on the stretcher members is magnified lessening the likelihood that the stretcher members and especially those at the wall front side will successfully resist such loadings and thus leading to fracture of the stretcher members. Where fracture occurs, the wall structure is not only weakened, but in the instance of a seawall is opened to the sea and consequent washing away of the fill, if any, within the wall and an undermining of the landfill behind the seawall so that total wall destruction invariably follows.
The crib block disclosed in U.S. Pat. No. 3,877,236 is of a design which is satisfactory in respect of its use in erection of certain kinds of wall structures. While more than adequate for such uses it does have a drawback in respect of use in walls subject to the heaviest types of loadings. The side panels of such unit extend below and behind the side panels of crib blocks next below. Moreover, the side panels of the unit are connected with a connecting arm that is of lesser height than the side panels so that if a massive force, e.g., earth pressure at the landside of a sea wall acts in a manner tending to slide the entire sea wall, force transmitted by one block to a like block next below (which one block is hooked at its panel bottom behind the top of the block below) is in the form of a cantilevering force which can fracture the panel of the block below away from its connecting arm. Furthermore, this form of block does not readily and conveniently allow for its use in erecting a staggered or stepped wall.
It is desirable therefore that there be provided a crib unit or block which is of heavy, rugged precast concrete construction having particularly enhanced resistance to bending and fracture in the side walls thereof and which is so constructed to possess identical loading resistance characteristics at both sides thereof. Furthermore it is desirable that the crib unit be such as to define or enclose when placed in side-by-side adjacency with a like crib unit, a bin enclosure characterized by the bin laterally narrowing at least in the outer reaches thereof transversely remote from the longitudinal centerline of the bin to an extent that preferably the bin course in such outer reaches approaches a circular course to thereby uniformly distribute bin fill pressure acting against the crib unit bin defining structure.